Re-sampling with phase offset adjustment for luma and chroma to select filters in scalable video coding

ABSTRACT

A sampling filter process is provided for scalable video coding. The process provides for re-sampling using video data obtained from an encoder or decoder process of a base layer (BL) in a multi-layer system using adaptive phase shifting to improve quality in Scalable High efficiency Video Coding (SHVC). In order to compensate for phase offsets introduced by downsampling an appropriate phase offset adjustment is made for upsampling in SHVC with an appropriate offset included for proper luma/chroma color space positions. In one approach the luma/chroma phase offset is specified and a filter is selected to apply the appropriate phase change.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a Continuation of U.S. patent application Ser. No.14/250,349, filed Apr. 10, 2014 which claimed priority under 35 U.S.C.§119(e) from an earlier filed United States Provisional Application Ser.No. 61/810,638 filed on Apr. 10, 2013, all of which are incorporatedherein by reference in their entirety.

BACKGROUND Technical Field

The present invention relates to a sampling filter process for scalablevideo coding. More specifically, the present invention relates tore-sampling using video data obtained from an encoder or decoderprocess, where the encoder or decoder process can be MPEG-4 AdvancedVideo Coding (AVC) or High Efficiency Video Coding (HEVC). Further, thepresent invention specifically relates to Scalable HEVC (SHVC) thatincludes a two layer video coding system.

Related Art

An example of a scalable video coding system using two layers is shownin FIG. 1. In the system of FIG. 1, one of the two layers is the BaseLayer (BL) where a BL video is encoded in an Encoder E0, labeled 100,and decoded in a decoder D0, labeled 102, to produce a base layer videooutput BL out. The BL video is typically at a lower quality than theremaining layers, such as the Full Resolution (FR) layer that receivesan input FR (y). The FR layer includes an encoder E1, labeled 104, and adecoder D1, labeled 106. In encoding in encoder E1 104 of the fullresolution video, cross-layer (CL) information from the BL encoder 100is used to produce enhancement layer (EL) information. The correspondingEL bitstream of the full resolution layer is then decoded in decoder D1106 using the CL information from decoder D0 102 of the BL to outputfull resolution video, FR out. By using CL information in a scalablevideo coding system, the encoded information can be transmitted moreefficiently in the EL than if the FR was encoded independently withoutthe CL information. An example of coding that can use two layers shownin FIG. 1 includes video coding using AVC and the Scalable Video Coding(SVC) extension of AVC, respectively. Another example that can use twolayer coding is HEVC.

FIG. 1 further shows block 108 with a down-arrow r illustrating aresolution reduction from the FR to the BL to illustrate that the BL canbe created by a downsampling of the FR layer data. Although adownsampling is shown by the arrow r of block 108 FIG. 1, the BL can beindependently created without the downsampling process. Overall, thedown arrow of block 108 illustrates that in spatial scalability, thebase layer BL is typically at a lower spatial resolution than the fullresolution FR layer. For example, when r=2 and the FR resolution is3840×2160, the corresponding BL resolution is 1920×1080.

The cross-layer CL information provided from the BL to the FR layershown in FIG. 1 illustrates that the CL information can be used in thecoding of the FR video in the EL. In one example, the CL informationincludes pixel information derived from the encoding and decodingprocess of the BL. Examples of BL encoding and decoding are AVC andHEVC. Because the BL pictures are at a different spatial resolution thanthe FR pictures, a BL picture needs to be upsampled (or re-sampled) backto the FR picture resolution in order to generate a suitable predictionfor the FR picture.

FIG. 2 illustrates an upsampling process in block 200 of data from theBL layer to the EL. The components of the upsampling block 200 can beincluded in either or both of the encoder E1 104 and the decoder D1 106of the EL of the video coding system of FIG. 1. The BL data atresolution x that is input into upsampling block 200 in FIG. 2 isderived from one or more of the encoding and decoding processes of theBL. A BL picture is upsampled using the up-arrow r process of block 200to generate the EL resolution output y′ that can be used as a basis forprediction of the original FR input y.

The upsampling block 200 works by interpolating from the BL data torecreate what is modified from the FR data. For instance, if every otherpixel is dropped from the FR in block 108 to create the lower resolutionBL data, the dropped pixels can be recreated using the upsampling block200 by interpolation or other techniques to generate the EL resolutionoutput y′ from upsampling block 200. The data y′ is then used to makeencoding and decoding of the EL data more efficient.

SUMMARY

Embodiments of the present invention provide systems for the upsamplingprocess from BL resolution to EL resolution to implement the upsamplingof FIG. 2. The upsampling process of embodiments of the presentinvention includes three separate modules, a first module to selectinput samples from the BL video signal, a second module to select afilter for filtering the samples, and a third module using phasefiltering to filter the input samples to recreate video thatapproximates the EL resolution video. The filters of the third modulecan be selected from a set of fixed filters each with different phase,or one or more adaptive or variable filters with a selectable phaseoffset.

For embodiments of the present invention luma and chroma phase offsetare separately accounted for in the filtering process. In oneembodiment, the luma and chroma offset used in the downsampling aredetermined and used to modify the phase offset determined for upsamplingand a filter chosen based on the combined offset.

The luma and chroma offsets can be separately accounted for in eitherhorizontal or vertical dimensions or both using the filters. The filterscan include separate row and column filters to enable parallel filterprocessing of samples along an entire row or column to accommodate asingle dimension offset corrections for luma and chroma.

A flag in syntax can be used to signal deblocking and SAO processing.For the case of AVC and HEVC, the BL pixel data used for re-sampling caneither be before or after the deblocking process. And for the case ofHEVC, the BL pixel data used can either be with or without SAOprocessing. For AVC and HEVC BL, a first syntax flag can be signaled toindicate whether the upsampling is performed on data that has beenpreviously deblocked. If the first flag is not set, then the upsamplingis performed on data prior to deblocking. If the first flag indicatesthat upsampling is to be performed on data that has been previouslydeblocked, a second syntax flag is further signaled to indicate whetherthe upsampling is to be performed on data that has been furtherprocessed with SAO. If the second flag is set, then the upsampling isperformed on data after SAO; otherwise, it is performed on data prior toSAO but after deblocking.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the present invention are explained with the help ofthe attached drawings in which:

FIG. 1 is a block diagram of components in a scalable video codingsystem with two layers;

FIG. 2 illustrates an upsampling process that can be used to convert thebase layer data to the full resolution layer data for FIG. 1;

FIG. 3 shows a block diagram of components for implementing theupsampling process of FIG. 2;

FIG. 4 shows components of the select filter module and the filters,where the filters are selected from fixed or adaptive filters to apply adesired phase shift;

FIG. 5 shows a table including syntax for signaling of luma and chromaphase shift offset that is signaled to select from fixed filters;

FIG. 6 shows a flow chart of simplified method steps for selectingfilters using luma and chroma phase offset in a first embodiment of thepresent invention;

FIG. 7 shows a table including syntax for signaling of luma and chromaadaptive filter parameters; and

FIGS. 8-9 show a flow chart of simplified method steps for signalingadaptive filters with luma and chroma phase offset in a secondembodiment of the present invention.

DETAILED DESCRIPTION I. Overview of Upsampling Circuitry for AdaptivePhase Correction

FIG. 3 shows a general block diagram for implementing an upsamplingprocess of FIG. 2 for embodiments of the present invention. Theupsampling or re-sampling process can be determined to minimize an errorE (e.g. mean-squared error) between the upsampled data y′ and the fullresolution data y. The system of FIG. 3 includes a select input samplesmodule 300 that samples an input video signal. The system furtherincludes a select filter module 302 to select a filter from thesubsequent filter input samples module 304 to upsample the selectedinput samples from module 300.

In module 300, a set of input samples in a video signal x is firstselected. In general, the samples can be a two-dimensional subset ofsamples in x, and a two-dimensional filter can be applied to thesamples. The module 302 receives the data samples in x from module 300and identifies the position of each sample from the data it receives,enabling module 302 to select an appropriate filter to direct thesamples toward a subsequent filter module 304. The filter in module 304is selected to filter the input samples, where the selected filter ischosen or configured to have a phase corresponding to the particularoutput sample location desired.

The filter input samples module 304 can include separate row and columnfilters. The selection of filters is represented herein as filters h[n;p], where the filters can be separable along each row or column, and pdenotes a phase index selection for the filter. The output of thefiltering process using the selected filter h[n;p] on the selected inputsamples produces output value y′.

II. Circuitry with Filter Selection for Adaptive Phase Correction

FIG. 4 shows details of components for the select sample module 302 ofFIG. 3 (labeled 302 a in FIG. 4) and the filters module 304 of FIG. 3(labeled 304 a in FIG. 4) for a system with fixed filters. For separablefiltering the input samples can be along a row or column of data. Tosupply a set of input samples from select input samples module 300, theselect filter module 302 a includes a select control 400 that identifiesthe input samples x[m] and provides a signal to a selector 402 thatdirects them through the selector 402 to a desired filter. The filtermodule 304 a then includes the different filters h[n;p] that can beapplied to the input samples, where the filter phase can be chosen amongP phases from each row or column element depending on the output samplem desired. As shown, the selector 402 of module 302 a directs the inputsamples to a desired column or row filter in 304 a based on the “Filter(n) SEL” signal from select control 400. A separate select control 400signal “Phase (p) SEL” selects the appropriate filter phase p for eachof the row or column elements. The filter module 304 a output producesthe output y′[n].

In FIG. 4, the outputs from individual filter components h[n;p] areshown added “+” to produce the output y′[n]. This illustrates that eachbox, e.g. h[0;p], represents one coefficient or number in a filter withphase p. Therefore, the filter with phase p is represented by all n+1numbers in h[0,p], h[n;p]. This is the filter that is applied to theselected input samples to produce an output value y′[n], for example,y′[0]=h[0,p]*x[0]+h[1,p]*x[1]+ . . . +h[n,p]*x[n], requiring theaddition function “+” as illustrated. As an alternative to adding inFIG. 4, the “+” could be replaced with a solid connection and the outputy′[n] would be selected from one output of a bank of P filtersrepresenting the p phases, with the boxes h[n:p] in module 304 arelabeled, for example, as h[n;0], h[n,1], h[n,p−1] and now each boxwould have all the filter coefficients needed to form y′[n] without theaddition element required.

In addition of how to configure the components of FIG. 4 to select inputsamples to add or combine coefficients to form y′[n] other modificationsto the circuitry of FIG. 4 can be made for additional embodiments of thepresent invention. Such modifications are described in the followingsections A-C.

A. Filters with Adaptive Phase Control

Although the filters h[n:p] in module 304 a are shown as separate phasefixed devices, they can be implemented using a single filter with phasep selected and adaptively controlled. The adaptive phase filters can bereconfigured by software. The adaptive filters can thus be designed sothat each filter h[n;p] corresponds to a desired phase p.

The filter coefficients h[n;p] can be signaled in the EL from theencoder so that the decoder can reconstruct a prediction to the FR data.Alternatively, a difference between the coefficients and a specified (orpredicted) set of coefficients can be transmitted. The coefficienttransmission can be made at some unit level (e.g. sequence parameter set(SPS), picture parameter set (PPS), slice, largest coding unit (LCU),coding unit (CU), prediction unit (PU), etc.) and per color component.Furthermore several sets of filters can be signaled per sequence,picture or slice and the selection of which set to be used forre-sampling can be signaled at finer levels, for example at picture,slice, LCU, CU or PU level.

B. Separable Column and Row Filtering

For the re-sampling process, in one embodiment the filters applied canbe separable, and the coefficients for each horizontal (row) andvertical (column) dimension can be signaled or selected from a set offilters. This is illustrated by the filters h[n;p] in FIG. 4 thatprovide separate filters for either an individual row or column. Theprocessing of row or columns separably allows for flexibility in filtercharacteristics (e.g. phase offset, frequency response, number of taps,etc.) in both dimensions while retaining the computational benefits ofseparable filtering.

The separable filtering in the re-sampling process can be specified asrow filtering first or column filtering first, as the order may affectthe memory or computational requirements. In the case of derivingfilters based on only the BL and FR data as described previously, notethat if row filtering and re-sampling is performed first, the estimationof the filters used for column filtering can be done based on there-sampled row data (or vice-versa). The filter coefficients can betransmitted in the EL, or a difference between the coefficients and aspecified (or predicted) set of coefficients can be transmitted.

C. Hardware and Software Modules for Circuitry

For the upsampling process components for FIG. 4, embodiments of thepresent invention contemplate that the components can be formed usingspecific hardware components as well as software modules. For thesoftware modules, the system can be composed of one or more processorswith memory storing code that is executable by the processor to form thecomponents identified and to cause the processor to perform thefunctions described.

III. Accounting for Luma and Chroma Offset

In SHM1.0, the upsampling process from the BL is performed usingseparable, fixed filters that are identical for each dimension. As aconsequence, the phase offsets for the filters used for interpolationare fixed. However, since downsampling is a non-normative process, it ispossible that upsampling with assumed, fixed phase offset filters maynot properly compensate for a phase offset introduced from downsamplingin each dimension. In particular, since luma and chroma components mayhave different color space resolutions, upsampling for the differentcolor components may require different phase offsets for each dimension.To address this issue, embodiments of the present invention propose twopossible solutions for SHVC.

A. Selecting a Filter Based on Normative Offset and Luma/Chroma Offset

The first embodiment provides for a selection of one of multiple filtersin FIG. 4 to account for luma and chroma offset. In the current SHM1.0,a set of 16 fixed filters with different phase offsets in the unitinterval can be specified. These filters are indexed where larger filterindices are used for larger phase offsets. In order to accommodate aphase offset introduced from downsampling required to maintain properluma/chroma color space positions after upsampling, it is proposed thatan offset parameter be signaled and used in computing the filter indexseparate from the normative offset. One example of this for the case of16 filters is shown in Table 1 of FIG. 5, where the signaling(highlighted) occurs at the PPS level. Note that the signaling can occurat other places within the PPS. Alternatively, signaling can bespecified at other levels, e.g. VPS, SPS, slice, PU, etc. Further,although offset adjustment is being accounted for in luma/chroma phasepositions, similar phase compensation can be made for color spaces,cropping, etc.

In Table 1, when cross-layer (CL) pixel prediction is allowed in an EL(e.g. nuh_layer_id>0 and a flag InterLayerTextureR1EnableFlag is set inSHVC Test Model 1), the four syntax elements listed below are signaled.Note that although specific logic syntax is shown in Table 1 to activatethe following four syntax elements, the following four syntax elements,as also shown in Table 1, can be signaled whenever CL prediction isenabled.

luma_phase_offset[0] indicates that the filter index used for upsamplingthe rows of the luma component should be obtained by addingluma_phase_offset[0] to the offset in the scaled grid, before computingthe final index. This is a signed value between −15 to +15 (given ascaled grid size of 16×).

luma_phase_offset[1] indicates that the filter index used for upsamplingthe columns of the luma component should be obtained by addingluma_phase_offset[1] to the offset in the scaled grid, before computingthe final index. This is a signed value between −15 to +15 (given ascaled grid size of 16×).

chroma_phase_offset[0] indicates that the filter index used forupsampling the rows of the chroma component should be obtained by addingchroma_phase_offset[0] to the offset in the scaled grid, beforecomputing the final index. This is a signed value between −15 to +15(given a scaled grid size of 16×).

chroma_phase_offset[1] indicates that the filter index used forupsampling the columns of the chroma component should be obtained byadding chroma_phase_offset[1] to the offset in the scaled grid, beforecomputing the final index. This is a signed value between −15 to +15(given a scaled grid size of 16×).

The above syntax is proposed for the Joint Collaborative Team on VideoCoding (JCT-VC), SHVC Test Model 1 (SHM 1) Section G.6.2 entitled“Derivation process for reference layer sample location used inresampling,” and in particular see J. Chen, J. Boyce, Y. Ye, M.Hannuksela, “Draft of SHVC Test Model Description,” JCTVC-L1007, January2013. The proposed text for SHVC G.6.2 includes information helpful inunderstanding the syntax, so it is modified as follows:

For the SHVC text in G.6.2, the inputs to this process are:

-   -   a variable cIdx specifying the color component index, and    -   a sample location (xP, yP) relative to the top-left sample of        the color component of the current picture specified by cIdx.

The output of this process is a sample location (xRef16, yRef16)specifying the reference layer sample location in units of 1/16-thsample relative to the top-left sample of the reference layer picture.

If cIdx is equal to 0, the variables xRef16 and yRef16 are derived asfollows:

xRef16=(xP*PicWRL*16+ScaledW/2)/ScaledW+luma_phase_offset[0]

yRef16=(yP*PicHRL*16+ScaledH/2)/ScaledH+luma_phase_offset[1]

Otherwise, the variables xRef16 and yRef16 are derived as follows:

xRef16=(xP*PicWRL*16+ScaledW/2)/ScaledW+chroma_phase_offset[0]

yRef16=(yP*PicHRL*16+ScaledH/2)/ScaledH+chroma_phase_offset[1]

Note that the syntax for this first embodiment concentrates on activityin FIG. 3 element 300 that selects samples to determine xRef16 andyRef16. The elements xRef16 and yRef16 are determined for downconvertedreference pictures that are identified in the select samples element300. The PicWRL is the picture width reference layer and the PicHRL isthe picture height reference layer, also identified in the selectsamples of element 300. The references to ScaledW for scaled width andScaledH for scaled height, however, are determined from the FR layer toenable a conversion back from the BL to calculate the EL pictureelements with phases set by xRef16 and yRef16. Note that a roundingoperation is used in the division operation by ScaledW and ScaledH inthe calculation of xRef16 and yRef16. The phase offset determined by theoperation for xRef16 and yRef16 first includes a portion divided byScaledW and ScaledH that will provide a normative phase offset, and theluma and chroma offsets are added to create the final phase values.

FIG. 6 shows a simplified flow chart for the above method steps fromTable 1 and syntax for determining xRef16 and yRef16 for selectingfilters using luma and chroma phase offset in this first embodiment ofthe present invention. In step 600, the cross layer (CL) prediction isexamined to determine if luma and chroma offset steps are to beconsidered. If so, the steps after 600 are processed. In steps 601 and602 the luma phase offset is determined for the rows and columns. Insteps 603 and 604, the chroma phase offset is determined for the rowsand columns. Finally in step 605 the xRef16 and yRef16 values aredetermined for both luma and chroma from the syntax described above.

The syntax elements allow for different phase offset shifts for luma andchroma as well as for horizontal and vertical directions. However,drawbacks of this first filter selection approach are that only a shiftin phase offsets is allowed, all 16 filters (or another fixed number inthe system) need to be specified, and the 16 phase offsets are fixed. Inaddition, rounding operations still need to be performed from desiredphase offsets to one the 16 fixed phase offsets. A proposed secondembodiment to address these issues is described in the next section.

B. Adapting Filter Based on Luma/Chroma Offset

The second embodiment provides for adjusting the phase offset based uponsignaling of adaptive filters. In order to allow for interpolationfilters with more general phase offsets and characteristics, instead ofre-indexing the filter index of existing fixed filters, this secondembodiment signals the filters with the desired phase offsets. Thefilter coefficients can be differentially signaled using existing HEVCfilters, such as the filters used for sub-pixel interpolation in HEVC.Other reference filters can also be used for differential coding of thecoefficients.

The Table 2 of FIG. 7 shows syntax for a proposed example for signalingat the PPS level for an embodiment where adaptive filtering offset canbe signaled. Note that the signaling can occur at other places withinthe PPS. As with the fixed filter embodiment of section A, for analternative signaling can be specified at other levels, e.g. VPS, SPS,slice, PU, etc.

As with the fixed filters of Table 1, in Table 2 of FIG. 7, whencross-layer (CL) pixel prediction is allowed in an EL (e.g.nuh_layer_id>0 and a flag InterLayerTextureR1EnableFlag is set in SHVCTest Model 1), the syntax elements for this embodiment are likewisesignaled. Note that although specific logic syntax is shown in Table 2to activate the following syntax elements, the following syntax elementscan be signaled whenever CL prediction is enabled. The syntax elementsfor adaptive filtering are as follows:

num_phase_offsets_minus1[0] plus one indicates the number of filterswith the desired phase offsets for the row upsampling process.

num_phase_offsets_minus1[1] plus one indicates the number of filterswith the desired phase offsets for the column upsampling process.

luma_pixel_shift_flag[i][j] indicates per dimension i (i=0, 1) andfilter phase index j (j=0, . . . , num_phase_offsets_minus1[i]), whetherthe filter is to be applied to shifted input luma samples. When thisflag is set to 1, the filter is applied to input samples that areshifted by one pixel; otherwise, input samples are not shifted.

ref_luma_filter_indx[i][j] indicates per dimension i (i=0, 1) and filterphase index j (j=0, . . . , num_phase_offsets_minus1[i]), the filterindex of one of the four HEVC reference filters used for sub-pixel lumainterpolation at 0, ¼, ½ and ¾ phase offsets.

delta_luma_filter_coef[i][j][k] indicates per dimension i (i=0, 1) andfilter phase index j (j=0, . . . , num_phase_offsets_minus1[i]) andfilter coefficient index k (k=0, . . . , num_luma_taps_minus1[i ]), theincremental value which should be added to the corresponding coefficientof the reference filter with index ref_luma_filter_indx[i][j] to obtainthe actual filter coefficients for the current filter phase index.

chroma_pixel_shift_flag[i][j] indicates per dimension i (i=0, 1) andfilter phase index j (j=num_phase_offsets_minus1[i]), whether the filteris to be applied to shifted input chroma samples. When this flag is setto 1, the filter is applied to input samples that are shifted by onepixel; otherwise, input samples are not shifted.

ref_chroma_filter_indx[i][j] indicates per dimension i (i=0, 1) andfilter phase index j (j=0, . . . num_phase_offsets_minus1[i]), thefilter index of one of the eight HEVC reference filters used forsub-pixel chroma interpolation at 0, ⅛, ¼, ⅜, ½, ⅝, ¾ and ⅞ phaseoffsets.

delta_chroma_filter_coef[i][j][k] indicates per dimension i (i=0, 1) andfilter phase index j (j=0, . . . , num_phase_offsets_minus1[i]) andfilter coefficient index k (k=0, . . . , num_chroma_taps_minus1[i]), theincremental value which should be added to the corresponding coefficientof the reference filter with index ref_chroma_filter_indx[i][j] toobtain the actual filter coefficients for the current filter phaseindex.

The values of num_luma_taps_minus1[i] and num_chroma_taps_minus1[i] perdimension i are set to 7 and 3, respectively. In general, these valuescan also be specified or signaled for each dimension.

To make operation more efficient, in some embodiments theluma_pixel_shift_flag[i][j] and a chroma_pixel_shift_flag[i][j] areimplemented. If the flag is set to 1, then the corresponding j_th lumaor chroma filter for dimension i is applied to input samples that areshifted by one pixel; otherwise, the input samples are not shifted.

The value of syntax elements ref_luma_filter_indx[i][j] orref_chroma_filter_indx[i][j] indicates one of four HEVC sub-pixel lumaor eight chroma interpolation filters that is used as a basis forprediction for the j_th luma or chroma adaptive phase offset filteralong dimension i. The k_th coefficient of the j_th filter alongdimension i for luma or chroma is modified by the adding the value ofdelta_luma_filter_coef[i][j][k] or delta_chroma_filter_coef[i][j][k].Together, these syntax elements specify the adaptive luma and chromafilters that are used to replace the fixed filters in Tables G-1 and G-2in SHVC Test Model 1. Note that Tables G-1 and G-2 in SHVC Test Model 1use 16 filters whereas in the proposed method the number of filters canbe specified by num_phase_offsets_minus1[i] in each dimension i.

In one embodiment, a set of default filters for upsampling can be agreedupon for the encoder and decoder. In the case that the default filtersare used, a flag can be set and signaled to indicate this. If the flagis not set, then the method described above can be used to signal thefilter parameters, and signaling of the filter coefficients can be basedon differential coding of the coefficients relative to the defaultfilters.

The semantics corresponding to the above syntax of Table 2 can bechanged in the draft Sections G.6.2, G.8.1.4.1.3 and G.8.1.4.1.4 (forLuma and Chroma sample interpolation process) of SHVC Test Model 1 (SHM1). It should be noted that the proposed derivation process no longerrequires rounding operations. The proposed text to help in understandingthe syntax, is as follows:

Inputs to this process are

-   -   a variable cIdx specifying the color component index,    -   a sample location (xP, yP) relative to the top-left sample of        the color component of the current picture specified by cIdx,

Output of this process is a sample location (xRef, yRef) specifying thereference layer sample location relative to the top-left sample of thereference layer picture, and phases (xPhase, yPhase).

1. The variables xRefphase and yRefphase are derived as follows:

xRefphase=(xP*PicWRL*(num_phase_offsets_minus1[0]+1))/ScaledW

yRefphase=(yP*PicHRL*(num_phase_offsets_minus1[1]+1))/ScaledH

2. The variables xRef and xPhase are derived by

xRef=(xRefphase/(num_phase_offsets_minus1[0]+1))

xPhase=(xRefphase−xRef*(num_phase_offsets_minus1 [0]+1))

3. The variables yRef and yPhase are derived by

yRef=(yRefphase/(num_phase_offsets_minus1[1]+1))

yPhase=(yRefphase−yRef*(num_phase_offsets_minus1[1]1+1))

Note that for certain values of num_phase_offsets_minus1[0] andnum_phase_offsets_minus1[1], the operations for computing xRef, xPhase,yRef, and yPhase may be performed by simpler operations (e.g. shift,&0x0F). Also, if the number of filters is restricted to be 2̂g, the indexg (instead of the value 2̂g) can be signaled to indicate 2̂g filters.Also, in order to account for negative phase offsets, the luma or chromavalues of xRef or yRef are decreased by one if the correspondingluma_pixel_shift_flag or chroma_pixel_shift_flag flags are set;otherwise the values of xRef or yRef are not modified.

As with the embodiment of Table 1, for the above syntax a concentrationis made on the select samples element 300 of FIG. 3, but also with thisembodiment calculations performed using syntax in filter selectionelement 302 is illustrated. The xRef and yRef are position locationsbased on downconverted reference pictures that are identified in theselect samples element 300. The xRef and yRef values are determinedusing xRefphase and yRefphase that are calculated in a similar matter tothe syntax shown previously relative to Table 1. The xRefphase andyRefphase values in this current embodiment will produce a remainderthat will be used to calculate the phase offsets xPhase and yPhase. ThexPhase and yPhase values are the phase offset values used to select afilter element in selection module 302 of FIG. 3. Because the filters inthis embodiment are adaptive, a rounding operation is not necessarilyrequired after calculations unlike with the previously describedembodiment.

FIGS. 8-9 shows a simplified flow chart for the above method steps fromTable 2 and syntax for determining xRef, yRef, xPhase and yPhase forsignaling adaptive filters with luma and chroma phase offset in thissecond embodiment of the present invention. In step 800, the cross layer(CL) prediction is examined to determine if luma and chroma offset stepsare to be considered. If so, the steps after 800 are processed. In steps801 and 802 the number of filters to be evaluated for phase offsetadjustment is determined along rows and columns. Next in a loop throughsteps 803-806 to consider the luma offset for each filter, a flagindicating if a pixel shift should be made is evaluated in step 804, areference luma filter is determined in step 805, and thedelta_luma_filter_coef values are used to modify the reference lumafilter in step 806. Further in steps 807-810, a similar loop isperformed to determine the chroma filters. Finally in steps 811-812 thexRef, yRef, xPhase and yPhase values are determined.

Benefits of this second embodiment include the following: (1) Arbitraryphase offsets are allowed in each dimension. (2) Better matching offilters and phases to scalability ratios other than 2x, 1.5x. (3) Lesscomputation needed since rounding operations to map a desired phase toone of the current fixed phases are eliminated. (4) Only the filters andphases necessary for performing the upsampling need to be signaled andindexed; there is no need to design and implement 16 luma and 16 chromafilters.

C. Deblocking and SAO Processing

Either of the embodiments illustrated with Table 1 or Table 2 can beimplemented whether deblocking or SAO processing is used. In theupsampling process, pixel data from the encode/decode process from theBL is used to generate a prediction for the FR pixel data. The BL pixeldata can be extracted, for example, at various points in the decodingprocess. For the case of AVC and HEVC, the BL pixel data used forre-sampling can either be before or after the deblocking process. Andfor the case of HEVC, the BL pixel data used can either be with orwithout SAO processing. In one embodiment for an AVC and HEVC BL, afirst syntax flag can be signaled to indicate whether the upsampling isperformed on data that has been previously deblocked. If the first flagis not set, then the upsampling is performed on data prior todeblocking. In addition, for the case of an HEVC BL, if the first flagindicates that upsampling is to be performed on data that has beenpreviously deblocked, a second syntax flag is further signaled toindicate whether the upsampling is to be performed on data that has beenfurther processed with SAO. If the second flag is set, then theupsampling is performed on data after SAO; otherwise, it is performed ondata prior to SAO but after deblocking. The signaling of the flags canbe made at some unit level (e.g. SPS, PPS, slice, LCU, CU, PU, etc.) andper color component, or it can be derived or predicted from otherpreviously decoded data.

Although the present invention has been described above withparticularity, this was merely to teach one of ordinary skill in the arthow to make and use the invention. Many additional modifications willfall within the scope of the invention as that scope is defined by thefollowing claims.

What is claimed:
 1. A system for scalable video decoding comprising: afirst decoding layer for decoding video with a base resolution; a seconddecoding layer for decoding video with an enhanced resolution having ahigher resolution than the base resolution; an upsampling unit receivingsampling signals from the first decoding layer and providing an outputsignal to the second decoding layer after an upsampling process, whereinthe upsampling unit output signal enables more efficient decoding in thesecond decoding layer, wherein the upsampling unit comprises: a firstmodule formed by code executable in a processor for selecting inputsamples of the video signal in the first decoding layer; a second moduleformed by code executable in a processor providing selection of aplurality of filters for processing the selected input samples; and athird module including the plurality of filters, the third module formedby code executable in a processor for filtering the selected inputsamples with the selected filters, the third module providing the outputsignal from the upsampling unit, wherein the first decoding layer isdownsampled from the second decoding layer, wherein a first phase offsetis generated to select one of the filters used in the upsampling processto provide the output signal from the upsampling unit, and wherein atleast one of luma phase offset and chroma phase offset in downsamplingis used to determine the first phase offset to select the one of thefilters in the upsampling process, wherein the luma phase offset and thechroma phase offset are specified for both row and column filtering, andwherein the a sample location xRef16 and yRef16 for the first module isdetermined with the luma phase offset for row denoted,luma_phase_offset[0], the luma phase offset for column denoted,luma_phase_offset[1], the chroma phase offset for row denoted,chroma_phase_offset[0], the chroma phase offset for column denoted,chroma_phase_offset[1], all considered using the following equations forluma offset:xRef16=(xP*PicWRL*16+ScaledW/2)/ScaledW+luma_phase_offset[0]yRef16=(yP*PicHRL*16+ScaledH/2)/ScaledH+luma_phase_offset[1] and thefollowing equations for chroma offset:xRef16=(xP*PicWRL*16+ScaledW/2)/ScaledW+chroma_phase_offset[0]yRef16=(yP*PicHRL*16+ScaledH/2)/ScaledH+chroma_phase_offset[1] whereinxP and yP are a sample location relative to a top left sample, PicWRL isthe picture width reference layer, PicHRL is the picture heightreference layer, and ScaledW and ScaledH are the scalable width andheight in the second decoding layer.
 2. The system of claim 1, whereinboth the luma phase offset and the chroma phase offset are determinedand included in the first phase offset to select the one of the filtersin the upsampling process.
 3. The system of claim 1, wherein theselection of a filter from the plurality of filters third module iscontrolled by selection from the second module based on the first phaseoffset determination.
 4. A method for scalable video decodingcomprising: receiving sampling signals from the first decoding layer andproviding an output signal to a second decoding layer that codes videowith an enhanced resolution having a higher resolution than the baseresolution; selecting input samples of the video signal in the firstdecoding layer for decoding video with a base resolution; selecting afilter from a plurality of filters for processing the selected inputsamples for an upsampling process; and filtering the selected inputsamples with the selected filter, wherein a first phase offset isgenerated to select one the filters used to provide the output in theupsampling process, and wherein at least one of luma phase offset andchroma phase offset is determined and included in the first phase offsetto select the one of the filters for the upsampling process, whereinboth the luma phase offset and the chroma phase offset are determinedand included in the first phase offset to select the filters for theupsampling process, wherein the luma phase offset and the chroma phaseoffset are specified for both row and column filtering, a samplelocation xRef16 and yRef16 is determined with the luma phase offset forrow denoted, luma_phase_offset[0], the luma phase offset for columndenoted, luma_phase_offset[1], the chroma phase offset for row denoted,chroma_phase_offset[0], the chroma phase offset for column denoted,chroma_phase_offset[1], all considered using the following equations forluma offset:xRef16=(xP*PicWRL*16+ScaledW/2)/ScaledW+luma_phase_offset[0]yRef16=(yP*PicHRL*16+ScaledH/2)/ScaledH+luma_phase_offset[1] and thefollowing equations for chroma offset:xRef16=(xP*PicWRL*16+ScaledW/2)/ScaledW+chroma_phase_offset[0]yRef16=(yP*PicHRL*16+ScaledH/2)/ScaledH+chroma_phase_offset[1] whereinxP and yP are a sample location relative to a top left sample, PicWRL isthe picture width reference layer, PicHRL is the picture heightreference layer, and ScaledW and ScaledH are the scalable width andheight in the second decoding layer.
 5. The method of claim 4, whereinboth the luma phase offset and the chroma phase offset are determinedand included in the first phase offset to select the filters for theupsampling process.
 6. The method of claim 4, wherein the selection of afilter from the plurality of filters third module is controlled byselection from the second module based on the first phase offsetdetermination.